1. Field of the Invention
The present invention generally relates to an authentication system for use with a main device capable of being connected with a certain unit selected freely by a user as is typical of a personal computer (PC) being connected with peripheral units such as a printer. More particularly, the invention relates to an authentication system which enables a main device to recognize whether a unit connected thereto is an authorized one in order to prevent any glitch or accident caused by an ineligible unit being connected to the main device.
2. Description of the Related Art
For example, one can carry and use a portable notebook PC (hereinafter referred to as the notebook PC) anywhere they like because the notebook PC generally has a battery pack or a battery power source incorporated therein as a standard unit. The battery pack employed in the notebook PC is composed of rechargeable batteries, and can be repeatedly recharged for reuse, but with a limited service life resulting from degradation caused by charge and discharge cycles, service conditions, storage environments and so on. The battery pack is to be replaced when the rechargeable battery has reached its service life or a battery pack having a larger capacity is desired for more hours of operation of the notebook PC. Although the replacement battery pack should be principally such an authorized one that the maker of the notebook PC approves, the notebook PC may be provided with an unauthorized replacement battery pack commercially available at a lower cost. Even an unauthorized battery pack can serve the notebook PC without causing any problem so long as the pack satisfies electrical requirements.
However, the lithium-ion rechargeable battery that is mainly employed as a rechargeable battery in the battery pack of a notebook PC uses a flammable organic solvent as its liquid electrolyte. It is thus important to ensure safety thereof, which is achieved not only by the rechargeable battery itself but also by a protective circuit for ensuring safety upon occurrence of abnormalities due to some reason. No problem would occur if the unauthorized battery pack has its rechargeable batteries and peripheral configuration equivalent to the authorized one; however, it is practically impossible to provide the entirely equivalent configuration. Accordingly, an inferior configuration is provided for cost-cutting purposes. It is thus necessary to take preventive measures against troubles which may be caused by the notebook PC incorporating an unauthorized battery pack or by the unauthorized battery pack itself.
From the aforementioned viewpoints, such a battery pack has been suggested which has a recognition function for distinguishing an authorized battery pack from an unauthorized one to reject the connection of the unauthorized one to the notebook PC when the unauthorized one has been connected thereto (e.g., Japanese National Publication of Translated Version of PCT Application, Publication No. 9-500520).
As shown in FIG. 6, the conventional technique disclosed in Japanese National Publication No. 9-500520 allows an application circuit (such as a notebook PC) 60 to generate a random number “a” when connected with a battery pack 61. The application circuit 60 then transmits the random number “a” to the battery pack 61 over a connection line, while performing a function calculation with a stored function operation equation b=g(a) using the random number “a.” On the battery pack 61 side, the same function calculation is performed as in the application circuit 60 with a stored function operation equation [c=f(a)] using the received random number “a,” and the calculation result “c” is sent back to the application circuit 60 side. The application circuit 60 compares the received calculation result “c” with the calculation result “b” obtained in the application circuit 60. If b=c, then the application circuit 60 recognizes that the battery pack 61 is an authorized one, thus permitting the connection of the battery pack 61. If b≠c, then the battery pack 61 is determined to be an unauthorized one, thereby deactivating the application circuit 60.
However, the aforementioned conventional technique allows the application circuit 60 and the battery pack 61 to perform the same function calculation, thus making it possible to read the information stored in a memory of the application circuit 60 or the battery pack 61 in order to imitate the function calculation. However, for the battery pack 61 with a microcomputer for performing the function calculation and a memory for storing the calculation procedure being integrated into an IC chip for the purpose of miniaturization, it is very difficult to read out the entirety or a required portion of the information. On the other hand, for the application circuit 60 being a notebook PC, the recognition function which is required only at the time of installation of the battery pack 61 is desirably realized without any unnecessary additional cost. That is, the microcomputer and the operating system (OS) of the notebook PC are desirably provided with functions of generating random numbers and performing the function calculation and a memory for storing the procedure of the function calculation or other procedures. However, copying the contents of the memory on the application circuit 60 side would permit the faking of the battery pack 61.